The use of intravascular medical devices has become an effective method for treating many types of vascular disease. In general, a suitable intravascular device, such as an intravascular catheter, is inserted into the vascular system of the patient and navigated through the vasculature to a desired target site. Using this method, virtually any target site in the patient's vascular system may be accessed, including the coronary, cerebral, and peripheral vasculature.
The catheter typically enters the patient's vasculature at a convenient location, such as a blood vessel in the neck or near the groin. Once the distal portion of the catheter (i.e., the portion farthest from the proximal handle of the catheter) has entered the patient's vascular system, the distal tip may be urged toward the target site by applying an axial force to the proximal portion of the catheter. Catheters having a relatively high level of pushability and kink resistance more effectively communicate this axial force.
Catheters frequently travel through the vascular system in a tortuous path, and are often required to change direction and to even double back on itself. The catheter may be “steered” by applying torsional forces to the proximal portion of the catheter. Catheters having a relatively high level of torqueability facilitate the steering process. Further, catheters having a relatively high level of flexibility are effectively conform to a patient's tortuous vascular system.
The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 5 mm. In view of the geometry of the patient's body, it is desirable to combine the features of torqueability, pushability, kink resistance, and flexibility into a catheter, which is relatively long and has a relatively small diameter. It is often desirable that the catheter have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also sometimes desirable that a catheter be relatively flexible and steerable, particularly near its distal end. Further, it is sometimes desirable that the lumen of the catheter provide a pathway through the catheter having a low friction surface.
The blood vessels in the brain frequently have an inside diameter of less than 3 mm. Accordingly, it is desirable that intravascular catheters intended for use in these blood vessels have an outside diameter which allows the catheter to be easily accommodated by the blood vessel. The path of the vasculature inside the brain is highly tortuous, and the blood vessels are relatively fragile. Accordingly, it is desirable that distal portion of a catheter for use in the brain be adapted to follow the highly torturous path of the neurological vasculature, for instance, by having increased flexibility.
As described above, it is desirable to combine a number of performance features in an intravascular catheter. It is desirable that the catheter have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also desirable that a catheter be relatively flexible, particularly near its distal end. The need for this combination of performance features has been addressed by building a catheter out of two or more discrete tubular members having different performance characteristics. For example, a relatively flexible distal section may be bonded to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member.
Reinforcement for elongate medical devices, such as catheters, typically includes several wires or other elongate bodies wrapped around a core and then encapsulated. The wires may be wound in multiple layers in different regions to adjust the degree of kink resistance. This type of design can lead to large device diameters and may not provide the appropriate amount of kink resistance and pushability for the system. Further, several design iterations may be required to balance the trade-offs in the various mechanical characteristics and to optimize the design. Moreover, because the wires are not interconnected, such reinforcement has poor torque transmission.
The above-mentioned performance features are also desirable in substantially solid intravascular devices, such as guidewires.